Electric lamp filament having a coiled-coil body portion with oriented offset legs,and method of manufacture

ABSTRACT

A COILED-COIL FILAMENT OF REFRACTORY METAL WIRE HAVING LONGITUDINALLY DEPENDING LEGS AT EACH END THAT ARE JOINED TO THE COIL BARREL BY OPEN PRIMARY TURNS WHICH ARE BENT THROUGH PREDETERMINED ANGLES. THE PRIMARY WINDING IS FORMED AS A CONTINUOUS COIL AND, AFTER THE SECOND COILING OPERATION HAS BEEN COMPLETED AND THE PRIMARY AND SECONDARY MANDRELS HAVE BEEN REMOVED, SELECTED PRIMARY AND SECONDARY MANDRELS THE TRANSVERSELY EXTENDING LEGS ARE BENT AROUND AN ABUTTING STATIONARY ANVIL TO REPOSITION THE LEGS.

United States Jacob F. Michael lnventor Paramus. NJ.

Appl. No. 648.430

Filed June 23, 1967 Patented June 28, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

ELECTRIC LAMP FILAMENT HAVING A COILED- COIL BODY PORTION WITH ORIENTED OFF-SET LEGS, AND METHOD OF MANUFACTURE 7 Claims, 7 Drawing Figs.

U.S. Cl 313/344, 313/345, 313/346, 29/25.14, 29/25.17, 29/25.18 1nt.Cl HOIj l/l6, H01j19/10,l-101k1/14 Field of Search 1. 313/344, 345, 346

[56] References Cited UNITED STATES PATENTS 2,167,765 8/1939 McGowan 313/344 2,359,302 10/1944 Curtis 176/40 2,329,126 9/1943 Lammers. 176/122 2,820,920 l/l958 Penon' 313/344 2,258,158 10/1941 Lewy 1 r 176/120 3,383,539 5/1968 Scoledge 313/113 Primary Examiner-John W. Huckert Assistant Exam iner-B. Estrin Attorneys-A. T. Stratton, W. D. Palmer and D. S. Buleza ABSTRACT: A coiled-coil filament of refractory metal wire having longitudinally depending legs at each end that are joined to the coil barrel by open primary turns which are bent through predetermined angles. The primary winding is formed as a continuous coil and, after the second coiling operation has been completed and the primary and secondary mandrels have been removed, selected primary turns in each of the then transversely extending legs are bent around an abutting stationary anvil to reposition the legsv PATENTEUJUN28I971 3588-579 INVENTOR Jacob F. Michael AGENT V ICLIKI'I'RIC LAMP FILAMI'IN'I' HAVING A ('(IILI'ID-(TIII. BODY PORTION WI'l'Il ()RlIiN'l'l-II) OFF-SET LEGS. AN!) MI'I'I'IIUI) OF MAN! FA("I'llRIl BACKGROUND OF'I'HE INVENTION This invention relates to electric lamps and has particular reference to a compact coiled-coil filament for an incandescent projection lamp and to an improved method for manufacturing such filaments.

Certain types of projection lamps now being marketed require low voltage so-callcd "CC6" filaments. These filaments comprise a refractory wire (viz. tungsten) helix having a coiled-coil body portion or barrel with longitudinally extending legs at each end. The legs are attached to the lead-in con doctors of the mount structure and hold the filament in horizontal position within the lamp envelope in front of an internal reflector. Heretofore it has been the standard practice to wind a primary turn in the middle of each of the legs at a much greater pitch to provide an open turn or break." The resulting temperature discontinuity in the legs reduced the operating temperature of the outer leg sections and the welded junctures thereof with the lead wires without an excessive heat drain on the end turns of the coil barrel. These open turns or breaks also served as a reference point for positively locating the ends of the tungsten or molybdenum inserts employed to short out and cool the leg ends. Such positive location of the leg inserts is required to properly control the rating of the filament.

However, since the aforesaid open turns in the primary winding are formed before the second coiling operation and must be accurately positioned in the legs of the coil after the secondary coiling operation has been completed, the latter operation had to be perfonned on manually operated equipment. Such special primary coiling and hand-wound secondary coiling are not only critical time-consuming operations but increase the manufacturing cost of the filaments and make it difficult to control the filament rating.

SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide a coiled-coil type filament that avoids the prior art manufacturing problems and which can be made on a mass production basis without affecting the quality or rating of the filaments.

A more specific object is the provision of a low voltage CC6 tungsten filament for an incandescent projection lamp which can be made on automatic primary and secondary coiling machines.

A further object is the provision ofa method for efiiciently manufacturing such filaments and bending preselected primary turns of the coil legs to reset the legs in the desired spatial relationship.

The foregoing objects and other advantages are achieved in accordance with the present invention by fabricating the coiled-coil filaments on continuous primary winding and automatic retractable-mandrel secondary winding machines. The resulting coils are placed in a jig and a preselected turn in each of the transversely extending legs is bent by suitable tools, such as a pair of bending knives and an anvil, through a predetermined angle to form the desired open turn or break in the legs and place the offset outer ends of the legs in longitudinally extending relationship with the coil barrel.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGS. 1 and 2 are front and side elevational views, respectively, of an incandescent projection lamp containing the im' proved coiled-coil filament of the present invention, portions of the envelope being removed to show the construction details of the filament and mount assembly;

FIG. 3 is an enlarged plan view of the filament and associated lead-in conductor portions of the mount along the line Ill-lll of FIG. 1;

FIG. 4 is a similar view of a prior art filament and mount assembly; and 1 FIGS. 5 to 7 are enlarged elevational views of one end of the filament showing various phases in the leg-bending operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. I and 2 there is shown a ISO-watt 2l'volt T12 projection lamp 10 having a tubular vitreous envelope 12 that has a domed top coated with a layei 13 of suitable opaque material and which contains an elliptical reflector 14 and the improved coiled-coil filament l6lof the present invention. The filament 16 is supported in a substantially horizontal position at the focal point of the reflectpr 14 by a pair of rigid lead-in conductors 22 that extend through a ceramic insulator 24 fitted into an opening in the reflector 14. As shown more particularly in FIG. 2, these conductors 22 are spot welded to upstanding support wires 26 which are, in turn, fastened to a pair of rigid pins 28 hermetically sealed through a vitreous disc or wafer 30 that is fused to and closes the mouth of the envelope I2. A pair of auxiliary support wires 32 fastened to tabs provided at the lower edge of the reflector I4 and to a pair of dummy pins 34 hermetically sealed through the wafer 30 securely anchor the reflector in place. A cylindrical metal base 36 having a keyed center post 38 is cemented to the sealed end of the envelope 12 in accordance with standard lamp-making practice. 1

The present invention resides in the improved coiled-coil filament l6 and this component will now be described in detail.

As will be noted in FIGS. land 2, the filament 16 has a coiled-coil body portion or barrel that consists of a plurality of secondary turns 17 and is terminated at each end by singly coiled straight leg portions 18 that extend in the direction of the axis of the coil barrel and are attached to the conductors 22. As viewed in FIGS. 1 and 2 the filament legs 18 are both disposed in a plane that is substantially tangent to the uppermost sides of the secondary turns 17 or top surface of the coil barrel. When viewed in a direction normal to this plane, as depicted in FIG. 3, the aforesaid legs 18 are disposed in two separate planes that are parallel to and spaced predetermined distances from the proximate sides of the coil barrel. The filament 16 is thus held in predetermined position relative to the reflector 14 by the offset legs 18 and lead-in conductors 22 to which they are welded.

As shown most clearly in FIG. 3, the legs 18 are joined to the respective end (or terminal secondary turns I7 by bent opened primary turns 19 that are located predetermined and equal distances beyond the proximate sides of the coiled-coil. An insert 20 of molybdenum or] tungsten is inserted into each of the legs 18 in accordance with standard practice to facilitate welding the legs to the conductors 22 and to cool them when the filament I6 is energized. These inserts are seated against the bent primary turns 19 which thus serve as stops. As will also be noted, the primary turns that define the ofiset leg portions 18 are of thle same diameter and have the same spacing as the primary turns in the coiled-coil body portion.

In contrast to the sharp angularly-offset coil legs 18 provided by the transversely bent primary turns 19 of the improved filament 16, a prior art filament 40 of the same size and rating (shown in FIG. 4) has a coiled-coil body portion that consists of the same number of secondary turns 41 but is terminated by longitudinally depending inner leg sections 42 that are joined to the coil barrel by leg segments that are gently tapered or bent in a smooth curve. Moreover, the inner leg sections 42 are joined by axially-extending open primary turns 43 to straight outer leg sections 44. The inserts 200 are located within these outer leg sections 44, and the latter are welded to the leads 22a.

FILAMENT MANUFACTURE AND LEG-BENDING OPERATION The coiled-coil filament lb of the present invention is manufactured by winding a fine tungsten wire around a mandrel of dissimilar metal, such as molybdenum, on an automatic primary-coiling machine to provide a composite wire having a continuous winding of uniformly spaced primary turns. This composite wire is then automatically wound about a second and larger mandrel on a secondary winding machine having a mechanically retractable mandrel. The transversely extending legs of the resulting helix are automatically cut on the secondary coiling machine so that, after the primary mandrel has been chemically dissolved in the usual manner, a leg 118 of predetermined length is left at each end of the coil ll6, as shown in H6. 5.

The partly fabricated coils 16 are then placed in a jig which has a pointed stationary anvil 46 that engages the outer surface of a preselected primary turn 19. The jig includes a pair of bending knives 47 and 4b which, when actuated by a suitable known mechanism (not shown), are inserted between the primary turn 19 and the adjacent primary turns from the opposite side of the leg 18'. in the embodiment here shown, a positioning bar 50 attached to the knife 4% is seated against the proximate side of the coil barrel. Thus, a line tangent to the secondary turns 17 is used as a reference line for gauging purposes and insures that same primary turn l9 (the third turn beyond the barrel in the case here illustrated) will be engaged by the anvil 46 and knives d7, 48. This, in turn, controls the total number of primary turns in the coil barrel and insures that the number of such turns in each filament is the same, within a tolerance of plus or minus one primary turn. The filaments are thus reproducible and have the same rating.

When the anvil 46 and knives 47 and 48 are properly positioned, the knives are again actuated and swung in opposite directions through an angle of approximately 90, as shown in FIG. 6, around the stationary pivot point established by the anvil 46. The primary turn ll9 is thus bent from its as-wound" configuration through an angle such that the portion of the embryonic leg 18 beyond the bent turn is disposed in the desired parallel relationship with the axis of the coiled-coil. The bending operation is repeated at the other end of the coil and the coil is removed from the jig. As is shown in FIG. 7, the finished coils 16 thus have a sharply offset leg 18 at each end that is joined to the coil barrel by a transversely bent and opened turn 19 which is spaced a predetermined and constant distance x beyond the barrel. The inserts 20 are then placed in the legs 118 and the filament M is ready for mounting.

As will be apparent from the foregoing, the objects of the invention have been achieved in that an improved coiled-coil filament for an electric lamp and an efficient method for making such filaments on a mass-production basis have been provided. Experience has shown that the elimination of the discontinuous primary winding and the manual secondary coiling operations effected by the present invention has reduced the manufacturing cost of 2l-volt CC6 filaments by approximately 65 percent without any adverse effect on the coil quality.

While a preferred embodiment has been disclosed, it is to be understood that various modifications can be made without departing from the spirit and scope of the invention.

lclaim:

l. A filament for an electric lamp comprising a helix that is formed from refractory metal wire and has:

a. a body portion comprising a coiled-coil consisting of a plurality of spaced secondary turns, and

b. a singly coiled elongated leg portion at each end that is integral with and extends longitudinally from said coiledcoil,

each of said leg portions comprising a plurality of spaced primary turns and being joined to the adjacent terminal secondary turn of said coiled-coil by a bend which is defined by a single opened primary turn that extends through an angle such that said leg portions are angularly offset with respect to the respective terminal secondary turns and the coiled-coil.

2. The lamp filament set forth in claim ll wherein;

said secondary turns are of uniform diameter and spaced along a predetermined axis, and

said angularly-offset leg portions extend longitudinally beyond the respective ends of the coiled-coil in the same general direction as said predetermined axis.

3. The lamp filament set forth in claim 1 wherein;

said coiled-coil is of linear configuration, and the opened primary turns that define said bends are so located with respect to one another that the coiled-coil contains a predetermined number ofprimary turns.

4. The lamp filament set forth in claim 3 wherein said angu larly offset leg portions are substantially straight and substantially parallel to one another and to the axis of the coiled'coil.

5. The lamp filament set forth in claim 4 wherein;

said linear coiled-coil is of substantially uniform diameter,

and

said angularly otfset leg portions are disposed in a plane that is substantially tangent to the secondary turns of said coiled-coil.

6. The lamp filament set forth in claim 5 wherein;

said refractory metal wire comprises tungsten,

the primary turns of said angularly ofiset leg portions and coiled-coil are of substantially the same diameter and have substantially the same spacing between turns, and

said offset leg portions, when the filament is viewed in a direction normal to said tangential plane, are disposed in planes that are parallel to and spaced predetermined distances from the respective sides of said coiled-coil.

7. The lamp filament set forth in claim 5 wherein;

said angularly-offset leg portions are fastened to a pair of spaced conductors which support the coiled-coil in predetermined spatial relationship with a reflector that comprises part of a mount assembly for an incandescent projection lamp, and

each of said leg portions contain a refractory metal insert that is seated against the respective bent primary turns. 

